1. Field of the Invention
This invention generally relates to a scanning arrangement in a scanner operative for repetitively scanning indicia having parts of different light reflectivity, for example, bar code symbols, and, more particularly, to operating such a scanning arrangement under low electrical power or mechanical power conditions to minimize usage of electrical power.
2. Description of Related Art
Various optical readers and optical scanners have been developed heretofore to optically read bar code symbols applied to objects in order to identify the object by optically reading the symbol thereon. The bar code symbol itself is a coded pattern comprised of a series of bars of various widths and spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting properties. The readers and scanners electro-optically decoded the coded patterns to multiple digit representations descriptive of the objects. Scanners of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,460,120; 4,607,156; 4,673,805; 4,736,095; 4,758,717; 4,760,248; 4,806,742; 4,808,804; 4,825,057; 4,816,661; 4,816,660; 4,835,374; 4,845,350; 4,871,904; 4,896,026; D-306,434; and D-306,435, as well as pending U.S. patent applications Ser. Nos. 193,265; 265,143; 265,149; 264,693; 367,335 and 392,207, all of said patents and patent applications having been assigned to the same assignee as the instant invention and being hereby incorporated herein by reference.
As disclosed in the above-identified patents and applications, a particularly advantageous embodiment of such a scanner resided, inter alia, in emitting a light beam, preferably a laser beam, emitted from a light source, preferably a gas laser or a laser diode, and in directing the laser beam to a symbol to be read. En route to the symbol, the laser beam was directed to, and reflected off, a light reflector of a scanning component. The scanning component moved the reflector in a cyclical fashion and caused the laser beam to repetitively scan the symbol. The symbol reflected the laser beam incident thereon. A portion of the incident light reflected off the symbol was collected and detected by a detector component, e.g. a photodiode, of the scanner. The photodiode had a field of view, and the detected light over the field of view was decoded by electrical decode circuitry into data descriptive of the symbol for subsequent processing. The cyclically movable reflector swept the laser beam across the symbol and/or swept the field of view during scanning.
There were several different types of scanning components disclosed in the above patents and applications. For example, U.S. Pat. No. 4,251,798 disclosed a polygonally-shaped multi-faced wheel having mirrored outer surfaces on each of its faces. The wheel was mounted for rotation so that each mirrored outer surface was, in turn, positioned in an optical path along which the incident laser beam was directed to the symbol to be scanned. An electrical motor continuously rotated the mirrored wheel at a uniform angular rate during scanning.
Other scanning components disclosed in U.S. Pat. No. 4,251,798 were a bimorph or ferroelectric-type oscillating element, as well as a speaker-type oscillating element, each element having an oscillatable mirror. In each case, electrical power was continuously applied to each scanning element in order to reciprocatingly oscillate the mirror.
U.S. Pat. Nos. 4,387,297 and 4,496,331 disclosed a high-speed scanning component including an electric motor operative for reciprocatingly oscillating a reflector in opposite circumferential directions relative to an output shaft of the motor. Here, again, electrical power was continuously applied to the motor during scanning. U.S. Pat. No. 4,387,297 also disclosed a penta-bimorph scanner which also required continuous electrical power during scanning.
The light reflector need not have been a single planar mirror, but, as described in U.S. Pat. No. 4,760,248, could have been an optical component having a construction which was part concave and part planar. The reflector could be driven by an electrical motor in alternate circumferential directions along arc lengths less than 360.degree. as described in U.S. Pat. No. 4,496,831, or, in a variant construction, could be rotated completely around an axis as described in U.S. Pat. No. 4,816,661.
In still another variant construction, as described in U.S. Ser. No. 193,265 filed May 11, 1988, rather than using a reflector to effect the scanning action, the reflector was eliminated altogether in a so-called "mirrorless" design in which one or more of the other scanner components were jointly or separately moved relative to one another to effect a reciprocating scanning action driven by an electrical motor. The other scanner components included a light source component, e.g. a laser diode, and/or optical components, e.g. a focusing lens, and/or the photodetector component, e.g. a photodiode.
In all of the above-described scanners, no matter whether a reflector or other scanner component was oscillated in alternate circumferential directions or completely around an axis of rotation, and no matter what the configuration of the resulting scan pattern on the symbol, e.g. a single scan line, a set of multiple parallel or intersecting scan lines, an X-shaped pattern, a Lissajous pattern, a curvilinear pattern (see U.S. Ser. No. 138,563 filed Dec. 28, 1987), etc., the scanning component was energized and driven by electrical power which was continuously applied during scanning. This represented a large electrical current drain, particularly when an electrical motor was employed as a prime mover since the motor drew the most electrical current of all the electrical components in the scanner. In scanners of the hand-held type, wherein substantially all of the scanner components, including a set of batteries, were mounted on-board a hand-held head, the high current drain reduced the working lifetime of the on-board batteries.
To round out this discussion, electro-optical wand- or pen-type readers have also been used to scan bar code symbols. These readers were manually positioned on, and dragged across, the symbol. These readers had no on-board scanning components. Scanning was effected by the user by the manual act of dragging a reader tip across, and in contact with, the symbol. In addition, non-contact hand-held heads have been proposed for reading symbols. Such non-contact heads were held at a distance from the symbol. However, scanning was effected not by any on-board scanning component, but by flicking one's wrist in a direction across the symbol.